ya sounds like a good plan with 1/2 inch on bottom and 1/4" on sides .... or if you're really concerned about weight you could just duct tape some heavy poly to form a 'U' bottom and protect the bottom from goup as well as part way up the walls. The lazy man's partial sled protector
Mountain, the only piece that has to be strong is the front board that protects you and your seats. if you design it right, the bottom and both sides are supported by the vehicle and can be very thin. It just makes it so much easier to get the wood in and out, and also really protects the inside of the vehicle. When I used to slide it in my Explorer I referred to it a a "Pick Up Truck Conversion".